avoid null reference

Author: smdn

src/Smdn.Net.AddressResolution/Smdn.Net.AddressResolution/MacAddressResolver.AddressResolution.cs

@@ -90,6 +90,9 @@ protected virtual async ValueTask<AddressTableEntry> SelectAddressTableEntryAsyn
     CancellationToken cancellationToken
   )
   {
+    if (predicate is null)
+      throw new ArgumentNullException(nameof(predicate));
+
     AddressTableEntry priorCandidate = default;
     AddressTableEntry candidate = default;